# std::source_location

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< cpp‎ | utility

Defined in header `<source_location>` |  |
struct source_location; |  | (since C++20)

The `std::source_location` class represents certain information about the source code, such as file names, line numbers, and function names. Previously, functions that desire to obtain this information about the call site (for logging, testing, or debugging purposes) must use macros so that predefined macros like __LINE__ and __FILE__ are expanded in the context of the caller. The `std::source_location` class provides a better alternative.

`std::source_location` meets the DefaultConstructible, CopyConstructible, CopyAssignable, Destructible and Swappable requirements.

Additionally, the following conditions are true:

- std::is_nothrow_move_constructible_v<std::source_location>,
- std::is_nothrow_move_assignable_v<std::source_location>, and
- std::is_nothrow_swappable_v<std::source_location>.

It is intended that `std::source_location` has a small size and can be copied efficiently.

It is unspecified whether the copy/move constructors and the copy/move assignment operators of `std::source_location` are trivial and/or constexpr.

### Member functions

##### Creation
(constructor) | constructs a new `source_location` with implementation-defined values (public member function)
current [static] | constructs a new `source_location` corresponding to the location of the call site (public static member function)
##### Field access
line | return the line number represented by this object (public member function)
column | return the column number represented by this object (public member function)
file_name | return the file name represented by this object (public member function)
function_name | return the name of the function represented by this object, if any (public member function)

### Notes

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_source_location` | `201907L` | (C++20) | Source-code information capture (`std::source_location`)

### Example

Run this code

    #include <iostream>
    #include <source_location>
    #include <string_view>

    void log(const std::string_view message,
             const std::source_location location =
                   std::source_location::current())
    {
        std::clog << "file: "
                  << location.file_name() << '('
                  << location.line() << ':'
                  << location.column() << ") `"
                  << location.function_name() << "`: "
                  << message << '\n';
    }

    template<typename T>
    void fun(T x)
    {
        log(x); // line 20
    }

    int main(int, char*[])
    {
        log("Hello world!"); // line 25
        fun("Hello C++20!");
    }

Possible output:

    file: main.cpp(25:8) `int main(int, char**)`: Hello world!
    file: main.cpp(20:8) `void fun(T) [with T = const char*]`: Hello C++20!

### See also

#line | changes the source code's line number and, optionally, the current file name (preprocessing directive)
stacktrace_entry (C++23) | representation of an evaluation in a stacktrace (class)

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